1. Field of the Invention
The present invention pertains to an improved system for conveying and collecting airborne particulate matter and is particularly adapted to be used in conjunction with earth drilling equipment for handling both the fine and coarse drill cuttings discharged from the drill hole.
2. Background Art
The increasing need to control airborne dust and particulate matter from various sources has resulted in a demand for equipment which is capable of handling large volumes of air heavily laden with dust and debris ranging from particle sizes which are kept airborne only by relatively high velocity flow streams to particles having a nominal dimension less than 4 to 5 microns.
There are many applications where improvements in conveying and collecting airborne dust and debris have been desired but one of the most demanding situations has been managing the material removed from the drillhole in various earth drilling operations. A widely used technique in drilling blast holes as well as exploratory shot holes and wells of various kinds, where conditions permit, involves the removal of the material from the hole by a high velocity stream of pressure fluid such as compressed air. In conventional drilling practice wherein localized crushing of the earth and rock is accomplished by a bit disposed at the lower end of an elongated drill stem the material removed during the formation of the drillhole comprises particulate matter ranging in size from nominal dimensions of 10 millimeters down to fine dust particles of less than 5 to 10 microns. This material is removed from the hole by compressed air which is conducted down into the hole within the hollow drill stem and is ejected at the bottom of the hole through orifices in the drill bit. The compressed air is supplied in sufficient quantity from a compressor either on board the drilling rig or connected thereto to enable the drill cuttings and dust to be ejected from the hole through the annular flow area between the bore wall and the drill stem. The demand for ever increasing rates of penetration and hole size has, of course, increased the size of compression equipment required so that adequate volumes of air are supplied to remove the drill cuttings from the hole to facilitate the drilling process.
The continuous ejection of large flow rates of air heavily laden with particulate matter of the consistency described above has been a long standing problem in the art of earth drilling epuipment. The problem associated with pollution and creation of health hazards from large quantities of airborne dust together with a desire to minimize contamination of the drilling equipment has resulted in numerous efforts to develop equipment to control the drill cuttings and dust ejected from the drill hole. Prior art methods of dust control and collection have generally involved the provision of an enclosure around the drillhole at the surface comprising a relatively large box-like hood having rigid side walls or flexible curtains which depend vertically to engage or be in closed proximity to the ground. Usually, a filter unit comprising one or more impingement type filter elements is also mounted on the drilling rig and connected to the aforementioned enclosure by a suitable conduit. Most known types of filter units require a suction pump or "blower" disposed downstream of the impingement type filter elements to assist in conveying the flow stream of dust laden air through the complete filtering system.
One long standing problem with prior art systems has been related to the fact that the heavier drill cuttings or being ejected from the drill hole fall to the ground within the enclosure or hood due to the reduced velocity of the conveying air stream as it enters the enlarged volume of the hood. These heavier cuttings usually form a somewhat volcano shaped pile around the drillhole which presents a problem in itself in most types of drilling. For example, if the piles of drill cuttings are not removed from the drillhole upon completion of the drilling operation the material is often accidentially pushed back into the hole by the movement of the hood or the drilling rig as it is moved from one drilling site to another, by other pieces of equipment used in the area of drilling and from natural activity such as high winds and/or rain. Accordingly, there has been a long felt need for drill cuttings conveying and handling systems which will remove all of the cuttings and dust from the immediate vicinity of the drillhole. This has become increasingly important in certain operations where the economic value of the cuttings is sufficient to warrant substantial reclamation of the cuttings and where drillholes are being formed for analysis of the cuttings themselves.
Not only has it become important to remove substantially all of the drill cuttings from the immediate vicinity of the drillhole but the desire to minimize airborne dust in the vicinity of drilling equipment, and for that any particular environment, has resulted in new demands for improvements in dust control and collection equipment. Prior art dust collecting hoods, particularly those involving loosely hanging flexible skirts or curtains, have proven to be generally inadequate to suitably contain and control fine dust being ejected from the drillhole. Even filter systems with suction pumps or blowers capable of handling an inlet air flow rate of between two and three times the volume flow rate of air being conducted down the drill stem have proven to be inadequate to control the escape of substantial quantities of dust laden air from around the drillhole.
Accordingly, the desire and need to provide for a total conveying and collection system for the entire range of particle size comprising the cuttings and "dust" generated in earth drilling operations has resulted in the development of a type of system in which so called make up air is provided at or near the point of ejection of the cutting flow stream from the drillhole. These relatively new systems are characterized by very high power requirements necessitated by suction fans or blowers which are required to handle an inlet flow capacity of as much as four to six times the nominal volumetric flow rate of air being conducted down the drill stem in order to assure that the heavier cuttings as well as the fine dust particles are conducted away from the vicinity of the drillhole. Some prior art collection systems involve the provision of an enclosed or hood around the drill stem in the vicinity of the drillhole disposed such that the lower edge of the hood is not in sealing engagement with the ground surface but is supported at a point above the ground so that ambient atmospheric air is drawn into the enclosure as the make up air which mixes with the flow stream of air and entrained particles emanating from the drillhole. This type of systems requires substantially more power for driving the suction blower than earlier systems and, due to the substantial increase in the amount of air being handled, requires larger and more expensive systems components including ducting, gravity and/or inertial separation equipment and larger impingement type filters for separation of the fine dust particles. Therefore, this type of total collection systems is expensive, presents new problems in regard to mounting on portable drill rigs due to the increased bulk and weight of the system, and requires a great deal more power than should be allocated to the function of cuttings and dust conveying and collection.
Another type of system using so called make up air provides an enclosure around the drill stem in the vicinity of the drillhole which is intended to be in sealing engagement with the ground surface and wherein make up air is drawn into the enclosure through an annular area between the drill stem and the upper surface of the enclosure or hood. Some of the prior art systems discussed herein are also provided with high pressure make up air by way of a separate conduit leading from the drill rig compressor directly to the interior of the hood. These systems require the drill rig bailing air compressor to be much larger and more powerful that the compressors provided on rigs already in use and, of course any new equipment must be designed to accomodate a larger compressor.
Prior art total collection systems of the type described hereinabove have also proven to be relatively sensitive to the ratio of total air flow to the amount of material being conveyed. If a proper relationship between the amount of make up air and total material flow rate is not maintained the system ducting and separating components tend to become plugged and they are sensitive to any accumulation of material in the area of the hood disposed around the drill stem.
Known types of dust collection systems for earth drilling equipment, including the known types of total collection systems, are also not well suited to operate with drilling equipment which is adapted for so called angle drilling wherein the axis of the drillhole is not perpendicular to the surface of the ground in the vicinity of the hole. In known types of drill cuttings collection systems the hoods or enclosures around the drillhole are not capable of providing a suitable seal regardless of the drilling angle or wherein the terrain in the vicinity of the hole is uneven or broken. This factor is particularly critical in regard to the total collection systems which utilized make up air drawn into the system from around the periphery of the lower edge of the hood. Moreover, in rotary drilling equipment wherein a so called pull down force or down thrust on the drill stem is used to control penetration rates the height of the drill rig deck plate and substructure will necessarily change depending on the drilling conditions. This again will effect the position of the hood or enclosure with respect to the ground surface which presents operational problems with the type of total collection system which uses make up air drawn into the hood between the ground surface and the lower peripheral edge of the hood.
Accordingly, there have been a number of problems in the art of dust conveying and collection systems adapted for use with earth drilling rigs for which solutions have not been found prior to the development of the present invention.
It should also be noted that another shortcoming of prior art dust collection equipment pertains to the arrangement of the portion of the enclosure or housing which provides for inertial separation of dust entrained in the moving air stream and its overall arrangement with respect to further structure which encloses the impingement type collection or filter elements. Prior art apparatus is generally characterized by a relatively large enclosure having an inlet for the dust laden air flow stream and which is of sufficient volume to substantially reduce the velocity of the flow as it enters the enclosure. The enclosure is usually divided into the primary separation chamber which accomplishes dust separation by change of direction of the flow stream together with a reduction in velocity of the air flow whereby the air with the remaining fine entrained dust flows into a second chamber and through one or more impingement type filter elements. The substantially clean air then flows through the suction fan or blower and to atmosphere. In a continuing effort to minimize the space requirements for dust collection equipment it has been discovered in accordance with the present invention that a unique compact arrangement of inertial separation flow chambers and impingement type filter elements may be provided which is highly efficient and is particularly suited for heavy dust loadings associated with earth drilling equipment. The improved inertial separation and filtration unit is also well suited to the total dust conveying and collection system of the present invention.